This is a submission of a revised application in which the investigators propose to study the relevance of CD8+ T cell mediated, non-cytotoxic and non-MHC-mediated suppression of human cytomegalovirus infection in human brain. As a result of the acquired immunodeficiency syndrome (AIDS) epidemic, there has been a dramatic increase in encephalitis produced by human cytomegalovirus (CMV), the most common opportunistic viral infection in AIDS patients. Intriguing preliminary studies performed in our laboratory have demonstrated that T lymphocytes, microglial cells, and selected cytokines potently inhibit CMV expression in productively infected primary human astrocytes, the most prevalent cell type in the brain. In this proposal, the central hypothesis to be tested is that CMV-specific T lymphocytes and microglial cells inhibit viral expression in brain cells through non-cytotoxic, non-MHC-restricted mechanisms mediated by the production of soluble factors. To test this hypothesis, the influence of T lymphocytes on CMV expression will be evaluated by determining if activated T cells from CMV-seropositive donors, as well as seronegative subjects, have the ability to suppress CMV gene expression in astrocytes. Through the use of transwell inserts, it will then be determined if the observed suppression of CMV expression is mediated through soluble factors. The addition of antibodies against specific cytokines will identify which soluble, inhibitory factors are involved. To determine if the suppressive ability of T lymphocytes can be mimicked by selected recombinant cytokines, the effect of exogenous cytokine treatment on CMV expression and replication in astrocytes will be examined. A human brain cell/athymic rat xenograft model will be used to investigate the antiviral effects of cytokine treatment in an in vivo model of human CMV infection in an enclosed, "immune privileged" site. To investigate the molecular mechanisms responsible for non-cytotoxic T cell and cytokine-induced viral suppression, their effect on the activation of transcription factors in astrocytes will be examined. Through the use of recombinant adenovirus vectors and reporter gene assays, it will be determined if these immune mediators lead to decreased CMV immediate-early gene promoter activity, thereby inhibiting the replication cascade. Finally, the role of microglial cells in controlling CMV infection of astrocytes will be addressed by determining if microglial cells suppress viral expression when co-cultured with CMV-infected human astrocytes and by measuring the production of antiviral cytokines from these cells in response to viral infection. Information gained from these studies will increase our understanding of the pathogenesis and host defense against this devastating central nervous system disease and may lead to innovative interventions for the management of AIDS-related CMV encephalitis based on immunotherapy.